Lapping apparatus and method



av z 'A TTORNE rs.

March 26, 1940. D. A. WALLACE LAPPING APPARATUS AND METHOD Filed June 6, 1938 Patented Mar. 26, 1940 UNITED. STATES PATENT OFFICE Chrysler Corporation,

Highland Park, Mich, a

corporation of Delaware Application June 6, 1938, Serial 9 Claims.

This invention relates to improved lapping apparatus and method and is a further development of the invention set forth in my co-pending application, Serial No. 107,377, filed October More particularly, the invention pertains to improvements in the feeding mechanism by which the pressure with which the lapping elements are. urged against the work is varied during the lapping cycle.

One of the important factors involved in efficient lapping of surfaces is the lapping pressure applied ments. Ifthe optimum unit lapping pressure, which varies with difierent materials and in some cases at difierent stages of the lapping operation, are substantially maintained or closely approached throughout the lapping operation, surfaces may be finished to a completely lapped state in much shorter time and with less relative lapping movements between the work and lapping elements than required when incorrect lapping pressures are applied. Since the area of contact between an unlapped surface and lapping elements increases as the roughness of such surface is decreased during lapping thereof, the employment of a uniform force of application between the lapping element and the work results in a decreasing unit lapping pressure as the lapping operation progresses.

It is one of the main objects of this invention to compensate in the force of application between the work and lapping elements for the increase in contact therebetween so as to maintain predetermined unit lapping pressures throughout the entire cycle of the lapping operation.

Another object of the invention resides in the provision of an improved lapping apparatus by which the pressure with which a lapping element is urged against a piece of work may be brought to different predetermined values at. diverse stages of a lapping cycle and without interrupting the lapping operation.

Other objects of the invention are to provide a lapping apparatus of this character in which the lapping pressure applied between the lapping element and the work varies in a predetermined relationship with respect to a relative movement between the-work and the tool; to provide means in apparatus of this kind for increasing the lapping pressure periodically after the lapping operation has continued throughout predetermined numbersof complete lapping movements or throughout a predeterminedtime inbetween the work and the lapping eleterval; and to provide means of this character in lapping apparatus which may progressively increase the lapping pressure at a predetermined rate as the lapping operation progresses from one stage to a more advanced stage.

Further objects of the invention are to pro-' vide a lapping apparatus of this kind by which the lapping element, while reciprocating at a relatively high speed approaching a vibratory or- ,der, is urged against a rotating piece of work with increasing pressure by control mechanism responsive to a predetermined number of rotations of the work; and to provide a pivotally mounted lapping element reciprocating member having. relatively extensible sections including a pressure actuated device for urging the aforesaid parts apart in order to vary the force of application of the lapping element carried thereby upon the work.

Additional objects of the invention are the provision or an improved lapping method in which efficient lapping is accomplished by so increasing the force of application between the lapping elements and the Work as to maintain the unit lapping pressure within a predetermined range of values during increasing of the area of contact between the work and lapping element; and to provide a method of this kind which is particularly adapted for use in connection with lapping apparatus of the type which has reciprocating lapping elements for operating upon a rotating piece of work.

Other objects and advantages of the invention will be more apparent from the following description taken in connection with the accompanying drawing, in which:

Fig. 1 is a side elevational view, partly in section, of lapping apparatus embodying the invention.

Fig. 2 is an enlarged, fragmentary, horizontal sectional view taken on the line 2-2 of Fig. 1 and showing the right end portion of the lapping apparatus. p

Fig. 3 is a transverse sectional view taken as indicated by the line 3-3 of Fig. 2.

Fig. 4 is a transverse, sectional view taken on the line 4-4 of Fig. 2.

Fig. 5 is a side elevational view of a cam which 'may be used in place of the cam shown in Fig. 2.

In the form of the invention illustrated in the drawing, the lapping apparatus, generally designated by the numeral 10, comprises a shank portion H, having spaced bearing recesses l2 and provided with cooperating bearing caps l3 for revolvably mounting the tool on a pair of crankthrow bearings I 4 of master crankshafts l5 and I 6 which are rotatably mounted in a machine bed structure (not shown).

A lever I1 is pivotally mounted at a location intermediate its end on the shank portion ll of the tool I 0 by a bolt l8 as illustrated in Fig. 1. The lever I1 is provided with an end portion IS on which a tool head 20 is axially slidably mounted. The tool head 20 has a clearance slot for the bolt l8 and also has a pair of H-shaped cross-sectional portions 2|, one of which is best shown in Fig. 4, which are guided on the end portion IQ of the lever, and held against removal from the latter by a pin 22' extending through a slot 23 formed in the intermediate portion of the lever l'l. The elongated slot 23 accommodates limited relative axial movement of the tool head 20 with respect to the lever ll. Formed in the end portion of the lever l1, opposite from the end portion l9 thereof is a cylindrical bore I 9' in which is disposed a piston 24 which is secured by the pin 22 to the tool head 20. The piston 24 is urged to the left, as viewed in Fig. 1, by a spring 26 bearing against the end wall of the end of the cylindrical bore l9. The left end of the bore I9 is suitably closed by a plug 21 and a sealing member 28 to provide a pressure tight cylinder which has a flexible conduit 30 leading thereto for admitting fluid pressure to cause the piston 24 to overcome the action of the spring 26, thereby urging the tool head 20 rightwardly as viewed in Fig. 1. v

The outer end portion of the tool head 20 is provided with a channel shaped recess 3! having a side wall 32 formed integral with the tool head and a detachable side wall, or flange 33, removably mounted on the tool head 20 by bolts 34. The side walls 32 and 33 of the recess 3! are provided with inwardly extending trunnions 35 on which a lapping member 35 is mounted. The lapping member 36 comprises a block 3'? having recesses 38 therein in which are securely mounted lapping elements 39 comprising natural stone, artificial compressed stone or other abrasive or lapping material. The lapping member 36 may be conveniently installed and removed from the tool head 20 by removal of the plate 33, the right end of which constitutes one wall of the recess 3|. A pair of spring-loaded detent members 40 act on respectively opposite sides of the right end portion I!) of the lever H to yieldably maintain the tool head 20 in its central position.

Formed in the left extremity of the lever I1 is an elongated slot having its maximum dimension extending in the direction of the axis provided by the bolt l8. The slot 45 accommodates a pin 46 eccentrically located on the lower extremity of a shaft 41 of a motor 48, mounted on the shank portion ll of the tool. The motor shaft 41 is rotatably journalled in spaced bearing members 49 and 50 carried by the shank H of the tool. The eccentrically located pin 46 of the motor shaft 47 has an external surface of generally spherical curvature which is adapted to operate upon the side walls of the elongated slot 45, during operation of the motor, in such a manner as to oscillate the lever I! about the axis provided by the bolt l8. e

During operation of thelapping tool, the motor 48 is preferably operated at a speed suificiently high to cause oscillatory movement of the lever I'I throughout a relatively short stroke and ,at a comparatively high speed approaching that of a. vibratory order. The lever I! in turn reciplocates the lapping member 36 and the lapping elements 39 at a correspondingly high speed.

The work comprises a crankshaft 5|, to which the lapping elements 39 are applied, which is preferably rotatively mounted with respect to an axis extending in a direction generally normal to l the axis of oscillatory movement of the lever I1. The crankshafts 5|, l5 and I6 are drivingly rotated in synchronism with each other as by a motor 52 having a pinion 53 meshed with a gear 54 detachably and non-rotatably secured to the work crankshaft 5|. The crankshaft l6 carries a gear 55 drivingly engaged with an idler gear 56 which also meshes with the gear 54.

The lapping elements 39 may be variably yieldably urged against the work by the admission of fluid pressure medium to the cylinder I9 through the inlet conduit 30 under the control of valve mechanism, generally designated by the numeral 64 in Fig. 1. The valve mechanism 64 may be operated in any desired manner to automatically vary the force with which the lapping elements are applied to the Work. In the illustration shown, this valve mechanism is operated in timed relationship to one of the relative lapping movements of the work and the lapping elements.

The valve mechanism 64 includes a casing 65 having a low pressure chamber 66 and a high pressure chamber 6'! communicatively connected by a passage 68 in which a variable valve 69 is mounted. The valve 69 has a tapering groove lil therein and it is normally urged leftwardly, as viewed in Fig. 1, toward its closed position by a spring H. Fluid pressure medium is fed under pressure into the high pressure chamber 61 by a pump 72 which draws fluid medium from a tank 73. When the valve 69 is opened, by-passing of fluid from the chamber 61 to the low pressure chamber 66 is accommodated and a corresponding reduction is produced in the pressure in the high pressure chamber 67 and in the cylinder IQ of the lapping element urging apparatus. By-passed fluid is returned from the low pressure chamber to the tank 73 through an outlet tube 14.

The valve 69 may be automatically actuated in any desired manner so as to vary the fluid pressure by which the lapping elements are urged against the work at predetermined intervals. In the form shown, this is accomplished by providing the valve 69 with a stem 15 having an end portion projecting externally of the casing 64 and carrying a cam following roller 16 which abuts against a cam 63. The cam 63 is non-rotatably fixed to a worm gear 6| having teeth meshed with a. worm that is driven by a shaft 58 and pinion 59. The pinion 59 is in turn driven by a gear 51 non-rotatably fixed to one of the main bearings of the master crankshaft l5, as

illustrated in Fig. 1.

The speed ratio reducing effect of the gearing may be predetermined to cause the cam 63 to complete one rotation in any desired lapping period which is preferably commenced while the valve 69 is fully open so as to gradually close the valve as the lapping cycle progresses, thereby gradually increasing the force applied by the fluid medium and piston 24 in urging the lapping elements against the work.' If desired, the cam 63 may be so contoured as to increase the force by which the lapping elements are urged against the work at a rate such that the tendency of the unit lapping pressure to decrease by reason of the increase in contacting area between the lapping element and the work, will be compen- ;ained, forexample, byv so constructing a cam ike that shown in Fig. 5 and its driving mechmisms as to apply a twenty pound pressure for ;he first five minutes of the lapping operation, a

.hlrty pound pressure during the next five minites, a forty pound pressure during the next five minutes, a sixty pound pressure during the next eight minutes and a one-hundred pound pressure during the last seven minutes of the lapping cycle. The lengths and numbers of diverse pressure periods may bepredetermined over substantially large ranges.

The time required to lap a piece of work is materially shortened by employment of the improved lapping apparatus and method. An optimum unit lap-ping pressure may be maintained throughout all stages of a lapping cycle even though the contacting area of the lapping element and work surface increases by reason of the removal of irregularities from the surface of the work as the lapping operation progresses.

Although but several specific embodiments of the invention are herein shown and described, it will be understood that various changes in the size, shape and arrangement of parts may be made without departing from the spirit of the invention.

What is claimed:

1. Surface finishing apparatus including a support for a piece of work, a tool having an abrading element engageable with said work, means for producing relative abrading movements including a relative rotative movement component between said work and said element, and mechanism for urging said abrading element and work together including means operable in timed relationship with respect to said relative rotative movement component of said abrading movements forincreasing the force by which said element and work are urged together from one value to a higher value without an accompanying intermediate decrease in said force during the progress of a finishing operation.

2. Lapping apparatus including a support for a piece of work, a lapping tool having a lapping element engageable with a surface of said work, means for rotating said work, and mechanism for holding said lapping element and work in contacting relationship ,with a predetermined force during the initial stages of a lapping operal tion including means operable in timed relationship to rotation of said work for progressively increasing said force as said lapping operation continues. r

3. Surface finishing apparatus including a sup- 5 port for a piece of work, a tool having an abrading element engageable with said work, means for producing relative movements between said work and said element, and mechanism for yieldably holding said lapping element and work in J contacting relationship including a resilient member and means operating upon said resilient member for urging said element and .said work together with a predetermined force during the initial stage of a lapping operation and in- 5 cluding control apparatus for said means adapted to increase said force at a subsequent stage of said lapping operation.

4. Surface finishing apparatus including a support for a piece of work, a tool having an abrading element engageable with said work, means 5 for producing relative movements between-said work and said element, and mechanism for yieldably holding said lapping element and work in contacting relationship including a resilient element and means for operating upon said resilil0 ent element with a predetermined force during the initial stage of a lapping operation and including variable control apparatus for said means adapted to intermittently increase said force at successive subsequent stages of said lapping operation.

5. Surface finishing'apparatus including a support, means on said support for rotatably supporting and'drivingly rotating a piece of work,

a tool fixture, an abrading tool having a main body portion movably mounted on said fixture and an abrading element carrier shiftably mounted on said main body portion for movement toward and away from said work, an abrading element mounted on said carrier, means for moving said main body' portion of said tool to'produce abrading movements of said element, fiuid pressure responsive mechanism mounted on said main body portion of said tool and operating upon said carrier for variably 39 urging said element against said work, and a fiuid pressure system connected with said mechanism including control means operable in timed relation with respect to rotation of said work for varying the pressure with which said element is urged against said work during operation of said apparatus.

6. Surface finishing apparatus including a support, means on said support for rotatably supporting and drivingly rotating a piece of work, a 40 tool fixture, an abrading tool having a main body portion movably mounted on said fixture and an abrading element carrier shiftably mounted on said main body portion for movement toward and away from said work, an abrading element mounted on said carrier, means for moving said main body portion of said tool to produce abrading movements of said element, fluid pressure responsive mechanism mounted on said main body portion of said-tool and operating upon said 60 carrier for variably urging said'element against said work, and a fluid pressure system connected with said mechanism including valve mechanism and control means so constructed and arranged as to progressively increase the force with which said element is urged against said work at predetermined intervals during an abrading operation.

7. The method of lapping a piece of work which comprises applying with a predetermined v force a lapping element to a surface of a piece of work to establish a predetermined unit lapping pressure during initial lapping of said surface, producing relative lapping movements including a relative rotative component movement between said lapping element and said surface, and gradually increasing said force at a rate proportional and in' timed relationship to the number of said relative rotatlve component movements.

8. Lapping apparatus including means for 7 rotatably supporting a piece of work, means for rotating said work, a fixture including means for reciprocably holding a lapping element in engagement with a surface of said work, driving means carried by said fixture'for reciprocating said lapping element during rotation of said work, and means for varying the lapping pressure in response to a predetermined number of rotations of said work.

9. Crankshaft lapping apparatus including a machine bed structure,-means thereon for rotatively supporting a crankshaft to. be lapped on its normal axis, a pair of master crankshafts rotatively mounted by said means about axes 10 substantially parallel to said normal axis and each being substantially identical in crank throw arrangement to said crankshaft to be lapped, means for driving said work crankshafts in synchronism with each other, a lapping tool supported by said first means having a lapping element adapted for engagement with the crank throw bearing 0! said work crankshaft, and means for varying'the'lapping pressure in response to movement of said master DAVID A. WALLACE. 

